A shirt that women use to make their titslook their biggest, usually only worn very occasionally
Girl A: hey what are you wearing to Sam's party?
Girl B: well i thought i might wear my tit top to remind everyone that im not flat.
Girl A: sounds like a plan!
When large breasts are squeezed into a clothing garment 2 sizes too small so that they look as if they will overflow and capsize at any moment just as the Titanic did.